1. Field of the Invention
The invention relates to a signal processor comprising an X-Y rotation circuit for rotating, consecutively, an input vector over a series of, in magnitude, decreasing phase angles into an output vector, said X-Y rotation circuit comprising first and second inputs for receiving the input vector, and first and second outputs for supplying the output vector, and a phase angle control circuit for decomposing an input phase into a series of, in magnitude, decreasing phase angles, said phase angle control circuit comprising a phase input for applying an input phase thereto.
2. Description of the Related Art
The invention further relates to a receiver comprising such a signal processor. Such a signal processor is known from IEEE Journal of Solid-State Circuits, Vol. 26, No. 11, Nov. 1991, p. 1645-1650. In this article, a signal processor, in the form of a Coordinate Rotation Digital Computer, is described, wherein an input vector is applied to the first and second inputs of the X-Y rotation circuit and a phase signal is applied to the phase input of the phase angle control circuit. An output vector, supplied to the first and second outputs, is formed by rotation of the input vector over an angle, which is an approximation of the phase signal, said approximation taking place in the phase angle control circuit. Such a signal processor can, for example, be used as a polar-to-cartesian converter, by applying a ramp-shaped signal to the phase input, having a range of 2.pi. radians. Now, the signal processor produces a cosine and a sine wave at the first and second outputs, respectively. In this way, the signal processor can be used as a mixing stage by applying a quadrature input signal to the first and second inputs.
A drawback of the known signal processor is that when a high frequency resolution is required, the phase signal needs to have a large word length, i.e., a large number of bits for representing the phase signal. This results in a large number of computations in the phase angle control circuit, resulting in a large and complex circuit.